1. Field of the Disclosure
This present disclosure generally relates to a pump. More specifically, it relates to a pump which forms thermal bubbles to transport liquid through a channel or deliver liquid from a reservoir to a channel of micro-fluidic devices. Resistive heaters configured to flow fluid in channels about a chip facilitate certain designs, as do techniques for controlling them. Thermal control facilitates other designs.
2. Description of the Related Art
Micro-fluidic devices manipulate microscopic volumes of liquid inside micro-sized structures. Applications of such devices include precise liquid dispensing, drug delivery, point-of-care diagnostics, industrial and environmental monitoring and lab-on-a-chip. Especially, lab-on-a-chip devices can provide advantages over conventional and non-micro-fluidic based techniques such as greater efficiency of chemical reagents, high speed analysis, high throughput, portability and low production costs per device allowing for disposability.
Micro-fluidic devices can be built by combining several components like channels, connectors, filters, mixers, chemical reactors, sensors, micro-valves, micro-fluidic pumps and etc. Among these components, it is well known to be difficult to attain micro-fluidic pumps which are ready to be assembled with micro-fluidic devices at low costs. For example, while a range of micro-fluidic devices have been miniaturized to the size of a postage stamp, these devices have often required large external pneumatic pumping systems for their operation. Moreover, to make portable and handheld point-of-care diagnostic and lab-on-a-chip devices, a small, reliable and disposable micro-fluidic pump is an indispensable component.
Micro-fluidic pumps generally fall into two groups: mechanical pumps and non-mechanical pumps. Mechanical pumps use moving parts which exert pressure on the liquid. Piezoelectric pumps and thermo-pneumatic pumps are included in this group. Usually, these pumps have complex structures and are difficult to manufacture at low costs. In addition, their size is large making them a major drawback for integration with smaller micro-fluidic devices. Among non-mechanical pumps, electro-osmotic pumps have been studied for micro-fluidic applications. An electro-osmotic pump uses surface charges that spontaneously develop when a liquid contacts with a solid. When an electric field is applied, the space charges drag a body of the liquid in the direction of the electric field. A disadvantage of this kind of pump is its high operation voltage and low flow rate.
Another example of a non-mechanical pump is a pump exploiting thermal bubbles. By expanding and collapsing either a bubble with diffusers or bubbles in a coordinated way, a thermal bubble pump can transport liquid through a channel. Several types of thermal bubble pumps have been proposed—for example, in U.S. Pat. No. 6,283,718 to Prosperetti (2001), U.S. Pat. No. 6,655,924 to Ma (2003) and U.S. Pat. No. 6,869,273 to Crivelli (2005). While the art described different ways to transport liquid using thermal bubbles, they failed to disclose how to make small, reliable and disposable pumps which are ready to be assembled with micro-fluidic devices at low cost. Moreover, the art overlooked the thermal effects of the thermal bubble pumps to the liquids transported. Since heat sensitive liquids are often used in micro-fluidic devices, the art is delinquent in understanding thermal aspects of thermal bubble pumps and should be considered. In addition, because properties of a liquid such as viscosity and energy required to generate the supercritical bubbles depend on the liquid temperature, a bubble pump needs to maintain the liquid temperature to a predetermined set point to control the pumping rate.
Thus, there is a need for a reliable and disposable micro-fluidic pump, which is ready to be combined with micro-fluidic devices. In addition, it is necessary to understand how to fabricate and operate a pump of this type to minimize the adverse thermal effects to the liquid transported.